The long range goal of the Mouse Mutant Gene Resource (MMGR) at The Jackson Laboratory is to provide a continuing source of new spontaneous mutations for biological and biomedical research. Spontaneous mutations in the mouse are the primary source of models for human conditions for which the mutated gene has not been cloned. The specific objectives of the MMGR program are to (1) identify new mutations in the mouse; (2) characterize the new mutants genetically, phenotypically, and pathologically; (3) establish the new mutations in strains suitable for further analysis by us and others; (4) preserve them as frozen embryos to assure their continued availability, and (5) provide mutants and controls to other investigators. The new mutations will be identified from among phenotypic deviants appearing in The Jackson Laboratory's breeding colonies. They will be characterized genetically by determining the mode of inheritance, testing for allelism with any already known mutations that produce similar phenotypes, and determining the chromosomal location. The new mutants will be characterized pheonotypically by observing their fertility, growth, viability, life span, and behavior and by defining their anatomical, histopathological, and physiological abnormalities. New mutants with potential for biomedical research will be maintained, preserved as frozen embryos, described in the open literature, and made available to other investigators at The Jackson Laboratory and in the world-wide scientific community.